Caption: Animation of the bonding in a molecule of ethane (C2H6). Initially there are two carbon atoms, each with full 1s and 2s electron orbitals (spheres), and one electron each in two 2p orbitals (blue and orange). These then undergo sp3 hybridisation, in which a 2s electron is promoted to the third vacant 2p orbital (red). The three 2p orbitals and the 2s orbital then hybridise, merging to form four sp3 orbitals (grey) arranged tetrahedrally around the carbon nucleus. Six hydrogen atoms then approach and form covalent bonds (blue) with three sp2 hybrid orbitals on each carbon, while the fourth sp3 hybrid forms a bond with its equivalent on the other carbon. These are called covalent s bonds.